Solid state electrolyte and electrode compositions

ABSTRACT

A lithium ion battery having an anode, a solid electrolyte, and a cathode. The cathode includes an electrode active material, a first lithium salt, and a polymer material. The solid electrolyte can include a second lithium salt. The solid electrolyte can include a ceramic material, a lithium salt, and a polymer material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional applicationSer. No. 14/584,841 filed Dec. 29, 2014 entitled “Solid StateElectrolyte and Electrode Compositions”, which claims priority to andthe benefit of U.S. Provisional Application No. 61/923,135 filed Jan. 2,2014 entitled “Solid State Electrolyte and Electrode Compositions”. Eachof these applications are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention is in the field of battery technology and, moreparticularly, in the area of solid polymeric materials and compositesfor use in electrodes and electrolytes in electrochemical cells.

Conventional lithium ion batteries include a positive electrode (orcathode as used herein), a negative electrode (or anode as used herein),an electrolyte, and, frequently, a separator. The electrolyte typicallyincludes a liquid component that facilitates lithium ion transport and,in particular, enables ion penetration into the electrode materials.

In contrast, so-called solid-state lithium ion batteries do not includeliquid in their principal battery components. Solid-state batteries canhave certain advantages over liquid electrolyte batteries, such asimprovements in safety because the liquids used in liquid electrolytesare often volatile organic solvents. Solid-state batteries offer a widerrange of packaging configurations because a liquid-tight seal is notnecessary as it is with liquid electrolytes.

Further, solid state batteries can use lithium metal as the anode,thereby dramatically increasing the energy density of the battery ascompared to the carbon-based anodes typically used in liquid electrolytelithium ion batteries. With repeated cycling, lithium metal can formdendrites, which can penetrate a conventional porous separator andresult in electrical shorting and runaway thermal reactions. This riskis mitigated through the use of a solid nonporous polymer electrolyte.

The electrolyte material in a solid-state lithium ion battery can be apolymer. In particular, poly(ethylene oxide) (“PEO”) can be used informing solid polymer electrolytes. PEO has the ability to conductlithium ions as positive lithium ions are solubilized and/or complexedby the ethylene oxide groups on the polymer chain. Solid electrolytesformed from PEO can have crystalline and amorphous regions, and it isbelieved that lithium ions move preferentially through the amorphousportion of the PEO material. In general, ionic conductivities on theorder of 1×10⁻⁶ S/cm to 1×10⁻⁵ S/cm at room temperature can be obtainedwith variations on PEO based electrolyte formulations. The electrolyteis typically formulated by adding a lithium ion salt to the PEO inadvance of building the battery, which is a formulation process similarto liquid electrolytes.

However, solid-state batteries have not achieved widespread adoptionbecause of practical limitations. For example, while polymericsolid-state electrolyte materials like PEO are capable of conductinglithium ions, their ionic conductivities are inadequate for practicalpower performance. Successful solid-state batteries require thin filmstructures, which reduce energy density, and thus have limited utility.

Further, solid-state batteries tend to have a substantial amount ordegrees of interfaces among the different solid components of thebattery. The presence of such interfaces can limit lithium ion transportand impede battery performance. Interfaces can occur (i) between thedomains of active material in the electrode and the polymeric binder,(ii) between the cathode and the solid electrolyte, and (iii) betweenthe solid electrolyte and the anode structure. Poor lithium iontransport across these interfaces results in high impedance in batteriesand a low capacity on charge or discharge.

Research on solid-state electrolyte materials tends to focus primarilyon the composition of the materials used to form the electrolyte toincrease ion conductivity. However, less attention has been paid tosolving the problem of increased impedance due to conductivity losses atinterfaces or addressing the transport of ions through the electrodestructures.

For example, U.S. Patent Publication 2013/0026409 discloses a compositesolid electrolyte with a glass or glass-ceramic inclusion and anionically conductive polymer. However, this solid electrolyte requires aredox active additive. As another example, U.S. Pat. No. 5,599,355discloses a method of forming a composite solid electrolyte with apolymer, salt, and an inorganic particle (such as alumina). Theparticles are reinforcing filler for solid electrolyte and do nottransport lithium. As yet another example, U.S. Pat. No. 5,599,355discloses a composite solid state electrolyte containing a triflatesalt, PEO, and a lightweight oxide filler material. Again, the oxidefiller is not a lithium ion conductor or intercalation compound.

More generally, ionically conductive polymers like PEO have beendisclosed with the use of a lithium salt as the source of lithium ionsin the solid electrolyte. For example, Teran et al., Solid State Ionics(2011) 18-21; Sumathipala et al., Ionics (2007) 13: 281-286; Abouimraneet al., JECS 154(11) A1031-A1034 (2007); Wang et al., JECS, 149(8)A967-A972 (2002); and Egashira et al., Electrochimica Acta 52 (2006)1082-1086 each disclose different solid electrolyte formulations withPEO and a lithium salt as the source for lithium ions. Still further thelast two references (Wang et al. and Egashira et al.) each discloseinorganic nanoparticles that are believed to improve the ionicconductivity of the PEO film by preventing/disrupting polymercrystallinity. However, none of these formulations address thelimitations of solid electrolytes and provide the performanceimprovements seen in the embodiments disclosed below.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide comparatively high capacityand low impedance in solid-state batteries, that is, batteries in whichthe electrodes and electrolyte are formed from solid materials and aresubstantially free of liquid components.

Embodiments of the present invention provide cathode materials andcomposites formed from certain lithium salts, for example lithiumbis(oxalato) borate or lithium bis(trifluoromethanesulfonyl)imide, usedin combination with poly(ethylene oxide), to improve capacity in asolid-state battery.

Embodiments of the present invention provide electrolyte materialsformed from certain lithium salts, for example lithium bis(oxalato)borate or lithium bis(trifluoromethanesulfonyl)imide, used incombination with PEO, to decrease impedance in a solid-state battery.

Embodiments of the present invention provide electrolyte materialsformed from certain lithium salts, for example lithium bis(oxalato)borate or lithium bis(trifluoromethanesulfonyl)imide, used incombination with PEO, to decrease the impedance of polymer/ceramiccomposite solid-state electrolytes.

Embodiments of the present invention include a lithium ion batteryhaving an anode, a solid electrolyte, and a cathode. The cathodecomprises an electrode active material, a first lithium salt, and apolymer material. The solid electrolyte can include a second lithiumsalt.

Embodiments of the present invention include a lithium ion batteryhaving an anode, a solid electrolyte, and a cathode. The solidelectrolyte comprises a ceramic material, a first lithium salt, and apolymer material. The solid electrolyte can include a second lithiumsalt.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A, 1B, and 1C illustrate schematic representations of cathode,electrolyte, and anode configurations according to certain embodimentsof the invention.

FIG. 2 illustrates improved capacity at a discharge rate of C/100 fromcells containing composite cathodes films formed from a polymer/lithiumsalt formulation and a polymer/lithium salt solid electrolyte accordingto certain embodiments of the invention.

FIG. 3 illustrates improved capacity at a discharge rate of C/1000 fromcells containing composite cathodes films formed from a polymer/lithiumsalt formulation and a polymer/lithium salt solid electrolyte accordingto certain embodiments of the invention.

FIG. 4 illustrates improved capacity in cells containing pressedcomposite cathodes films formed from a polymer/lithium salt formulationand a polymer/lithium salt solid electrolyte according to certainembodiments of the invention.

FIG. 5 illustrates the measured ionic conductivity of variouspolymer/lithium salt films according to certain embodiments of theinvention.

FIGS. 6A and 6B illustrate measurement of the impedance of filmscontaining polymer/lithium salt formulations according to certainembodiments of the invention.

FIGS. 7A and 7B illustrate measurement of the time dependence ofelectrical impedance of films containing polymer/lithium saltformulations according to certain embodiments of the invention.

FIG. 8 illustrates measurement of the ionic conductivity of filmscontaining ceramic/polymer/lithium salt formulations according tocertain embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions apply to some of the aspects described withrespect to some embodiments of the invention. These definitions maylikewise be expanded upon herein. Each term is further explained andexemplified throughout the description, figures, and examples. Anyinterpretation of the terms in this description should take into accountthe full description, figures, and examples presented herein.

The singular terms “a,” “an,” and “the” include the plural unless thecontext clearly dictates otherwise. Thus, for example, reference to anobject can include multiple objects unless the context clearly dictatesotherwise.

The terms “substantially” and “substantial” refer to a considerabledegree or extent. When used in conjunction with an event orcircumstance, the terms can refer to instances in which the event orcircumstance occurs precisely as well as instances in which the event orcircumstance occurs to a close approximation, such as accounting fortypical tolerance levels or variability of the embodiments describedherein.

The term “about” refers to the range of values approximately near thegiven value in order to account for typical tolerance levels,measurement precision, or other variability of the embodiments describedherein.

A “C-rate” refers to either (depending on context) the discharge currentas a fraction or multiple relative to a “1 C” current value under whicha battery (in a substantially fully charged state) would substantiallyfully discharge in one hour, or the charge current as a fraction ormultiple relative to a “1 C” current value under which the battery (in asubstantially fully discharged state) would substantially fully chargein one hour.

Ranges presented herein are inclusive of their endpoints. Thus, forexample, the range 1 to 3 includes the values 1 and 3 as well as theintermediate values.

Solid-state batteries can be formed using polymeric materials with ionconducting properties. The polymeric materials can be used in the solidelectrolyte. The polymer should have suitable mechanical properties andthermal stability, in addition to the desired level of ionicconductivity, and specifically lithium ion conductivity. As with otherapplications using polymeric materials, the properties of the solidstructure can be influenced by (i) the choice of polymer, (ii) themolecular weight of the polymer, (iii) the polydispersity of thepolymer, (iv) the processing conditions, and (v) the presence ofadditives.

Poly(ethylene oxide) (“PEO”) is a suitable polymer for use in lithiumion solid-state batteries. PEO is a commodity polymer available in avariety of molecular weights. PEO can range from very short oligomers ofabout 300 g/mol (or 300 Da) to very high molecular weights of 10,000,000g/mol (or 10,000 kDa). At molecular weights of 20 kDa and below, PEO istypically referred to as poly(ethylene glycol) or PEG. PEO has been usedas a separator in conventional liquid electrolyte systems and, asdescribed above, as a component in a thin film solid electrolyte.

PEO processed into a structure can have both crystalline and amorphousdomains. Ionic conductivity happens more readily in the amorphousdomains and, therefore, processing conditions that decrease crystallinedomain size and/or the overall amount of crystallinity are preferred.Some research has used carbonate solvents, such as ethylene carbonate,dimethyl carbonate, or diethyl carbonate, as plasticizers to improveionic transport and reduce interfacial impedance. However, this involvesthe addition of a volatile, flammable liquid to the battery and negatesmuch of the safety benefits brought by a solid-state electrolyte. In PEOsystems, PEG can be added to achieve the desired processing properties,such as a preferred solution viscosity, film modulus, or film glasstransition temperature.

While PEO is discussed herein as a preferred polymeric material, it isunderstood that other polymers with equivalent chemical,electrochemical, mechanical, and/or thermal properties can be used inplace of or in addition to PEO and/or PEO/PEG mixtures. Further,copolymers that include PEO, PEG, or PEO-like polymers in at least onesegment of the copolymer can be suitable for certain embodimentsdescribed herein. Thus, the embodiments described herein that refer toPEO or PEO/PEG are understood to encompass other such polymeric andco-polymeric materials.

According to some aspects discussed herein, certain lithium salts addedto polymeric materials improve the performance of solid-state batteries.Specifically, a lithium salt concentration in a PEO such that the etheroxygen (EO) to lithium ion ratio is about 3.1 (that is, [EO]:[Li⁺]=3:1)results in maximum ionic conductivity in the PEO films. In embodimentsdisclosed herein, the [EO]:[Li⁺] ratio varies from about 2:1 to about4:1, but is preferably about 3:1 to achieve the desired conductivity.Mechanical properties of the lithium salt/polymer composites arecontrolled by the molecular weight of the PEO, the ratio of PEO/PEG, andthe process used to make the film (e.g., the type and nature of thesolvent used for casting).

Suitable lithium salts include, but are not limited to, lithium triflate(LiCF₃SO₃), lithium tetrafluoroborate (LiBF₄), lithiumhexafluorophosphate (LiPF₆), lithium hexafluoroarsenate (LiAsF₆),lithium bromide (LiBr), lithium chlorate (LiClO₃), lithium nitrate(LiNO₃), lithium bis(oxalato)borate (LiB(C₂O₄)₂) (also referred toherein as “LiBOB”), lithium difluoro(oxalato)borate (LiC₂O₄BF₂), lithiummetaborate (Li₂B₄O₇), lithium bis(trifluoromethanesulfonyl)imide(CF₃SO₂NLiSO₂CF₃) (also referred to herein as “LiTFSI”), andcombinations thereof. In preferred embodiments, the lithium salt islithium triflate, LiBOB, LiTFSI, or combinations thereof.

As discussed above, additives can be used to favorably influence theproperties of the final polymer structure. The addition of lithium saltsto PEO can result in favorable thermal properties for the resultingmixture of salt and polymer.

For example, Table 1 provides the results of Differential ScanningCalorimetry testing of various salt and polymer combinations. Themolecular weight (MW) of the PEO is provided in the first column inkiloDaltons. The identity of the lithium salt additive is provided inthe second column. Note that the first row is a polymer formulationwithout any added lithium salt. The ratio of PEO:PEG:Salt (weight %) isprovided in the third column. The melt onset temperature (T_(m) onset),and peak melt temperature (T_(m) peak) are provided in the final twocolumns. Table 1 demonstrates that the ratio of PEO:PEG was about 4.26and was the same for all salt loading levels. Also, the 4.26 PEO:PEGratio was maintained for the different molecular weights of PEO used inthis testing. Thus, the thermal differences among the testedformulations can be attributed to the presence of the salt.

TABLE 1 Thermal Data for PEO/Salt Combinations Formulation T_(m) T_(m)PEO MW PEO:PEG:Salt (onset) (peak) (kDa) Salt (weight %) (° C.) (° C.)7,000 None 81:19:0  59 67 7,000 LiBOB 72.9:17.1:10 53 64 7,000 LiBOB64.8:15.2:20 34 54 8,000 LiBOB 64.8:15.2:20 32 55 7,000 Li Triflate64.8:15.2:20 57 65 8,000 Li Triflate 64.8:15.2:20 58 66

The addition of Li triflate to the PEO/PEG mixture did not have asignificant effect on the thermal properties of the PEO/PEG as comparedto the control. That is, the values for the onset of the meltingtemperature and the peak melting temperature remained similar to theunloaded PEO/PEG regardless of the molecular weight of the PEO.

However, the addition of LiBOB salt to the PEO/PEG mixture resulted in adecrease in the onset of the melting temperature and a decrease in thepeak melting temperature of the original polymer. Specifically, a 10%LiBOB loading level decreased the onset of the melting temperature andthe peak melting temperature. A 20% LiBOB loading level furtherdecreased the onset of the melting temperature and the peak meltingtemperature of the mixture. At a 20% LiBOB loading level and a slightlyhigher molecular weight PEO, the decrease versus control in the onset ofthe melting temperature and the peak melting temperature was maintained.

The decrease in the onset of the melting temperature and the peakmelting temperature is consistent with the LiBOB acting as a solidplasticizer for the PEO/PEG mixture. Therefore, if the ionicconductivity in the polymer is increased due to the plasticization, novolatile or liquid plasticizer was actually required. As described inmore detail below, the benefit of LiBOB in improving the cell capacityis observed for all the molecular weights of PEO tested.

Using the formulations of polymer and salt generally described above,electrolyte structures and electrode structures can be formed forlithium ion batteries. In certain aspects, solid electrolytes are formedfrom a polymer and a lithium salt. The inclusion of a lithium salt, suchas those disclosed herein and their equivalents, can improve theperformance of solid-state batteries by the mechanism disclosed hereinand other equivalent mechanisms. For example, the inclusion of LiBOB orLiTFSI in a PEO/PEG mixture can increase the conductivity of lithiumions through a PEO/PEG structure and can reduce the interfacialimpedance between the electrolyte structure and the electrode structure.

FIG. 1A depicts a schematic representation of a solid-state battery. Thecathode 10 includes domains of active material 10 a and domains ofconductive carbon 10 b. A binder may also be present in the cathode 10but is not pictured. The active material can be any active material ormaterials useful in a lithium ion battery, including the activematerials in lithium metal oxides or layered oxides (e.g.,Li(NiMnCo)O₂), lithium rich layered oxide compounds, lithium metal oxidespinel materials (e.g., LiMn₂O₄, LiNi_(0.5)Mn_(1.5)O₄), olivines (e.g.,LiFePO₄, etc.). Active materials can also include compounds such assilver vanadium oxide (SVO), metal fluorides (e.g., CuF₂, FeF₃), andcarbon fluoride (CF_(x)). More generally, the active materials forcathodes can include phosphates, fluorophosphates, fluorosulphates,silicates, spinels, and composite layered oxides.

In some embodiments, polymer/lithium salt materials and compositesdescribed herein are used in the formation of anodes. Appropriate activematerials for use in such anodes include, but are not limited to,graphitic and non-graphitic carbons, silicon and silicon alloys, lithiumtin oxide, other metal alloys, and combinations thereof.

In FIG. 1A, the solid electrolyte structure 20 is formed from any of thepolymer/lithium salt formulations disclosed herein. The solidelectrolyte structure 20 is depicted as a uniform and monolithicstructure, but other configurations are possible. The anode 30 isdepicted in FIG. 1A and can be a lithium metal anode, for example. Thesolid polymer electrolyte can include dispersions of nanoparticles 30 a,which may be incorporated to improve ionic conductivity or mechanicalproperties.

The loading of the lithium salt in the polymeric material of solidelectrolyte structure 20 provides improved lithium ion conduction ascompared to an unloaded polymeric material. Further, lithium iontransport across the electrolyte/anode interface 25 can be enhanced bythe lithium salt loaded solid electrolyte structure 20. The presence ofthe solid electrolyte structure 20 according to embodiments disclosedherein reduces the impedance in the battery and improves the batterycapacity.

In certain aspects, cathodes for solid-state batteries are formed froman active material, a polymer, and a lithium salt combination. Thecombination of lithium salts and PEO (or PEO/PEG) can be incorporated inthe cathode structure. The advantages of improving ion transport anddecreasing interfacial impedance are also important within cathodes.

One of the benefits of liquid-containing batteries is that a liquidelectrolyte can penetrate the porous space of a cathode and provide ionconduction paths. It is this benefit that perpetuates the use ofvolatile liquid organics despite their safety issues. A solid-statebattery does not have liquid to facilitate ion transport from within thecathode material.

Advantageously, embodiments of the polymer/lithium salt formulationsdisclosed herein can be used as additives during the formation ofcathodes. FIG. 1B depicts a schematic representation of a solid-statebattery which has an anode 30, a solid electrolyte structure 20, and aelectrolyte/anode interface 25 similar to that depicted in FIG. 1A. FIG.1B depicts a cathode structure 10 that includes domains of activematerial 10 a and domains of conductive carbon 10 b. The cathodestructure 10 further includes domains of a polymer/lithium saltformulation 15. While FIG. 1B depicts the components of cathode 10 asdiscrete domains, it is understood that processing steps (such asheating, dissolution, and/or pressure) can be used to create moreintimate mixing of the cathode components. During such mixing,interfaces will be formed among the domains of the cathode.Advantageously, the polymer/lithium salt formulations can reduce theinterfacial impedance in the cathode. Further, while the domains aredepicted with a particle-type configuration, the domains can be in otherconfigurations, including for example interpenetrating layers and/orfilms.

Further, FIG. 1B depicts domains of a polymer/lithium salt formulation15 and the solid electrolyte structure 20 with a different pattern. Thispattern difference indicates that the actual formulation of thepolymer/salt for use in the cathode may be different from theformulation for use in the solid electrolyte. For example, parametersincluding (i) the molecular weight of the PEO, (ii) the ratio of PEO toPEG, (iii) the loading of salt; (iv) the choice of salt or salts; and(v) the polymer/salt formulation processing conditions can be variedand/or optimized for use in the cathode as compared to the parametersselected for use in the electrolyte.

In some aspects, solid state batteries according to embodiments hereincan have no lithium salt additive loaded in the solid electrolyte if thecathode material includes polymer/lithium salt formulations. Theadditive lithium salt within the cathode can migrate out into the solidelectrolyte over time and provide benefits such as increased capacityand decreased impedance to the overall battery. Still further, the saltin the solid electrolyte can be different from the salt in thepolymer/salt formulation in the cathode. For example, lithium triflatecan be used in the electrolyte (with a polymer such as PEO or PEO/PEG)and LiBOB or LiTFSI can be used in the cathode (with a polymer such asPEO or PEO/PEG).

Embodiments of the polymer/lithium salt formulations disclosed hereincan be used as additives during the formation of composite solidelectrolytes. FIG. 1C depicts a schematic representation of asolid-state battery which has an anode 30 and a cathode 10 similar tothat depicted in FIG. 1B. In FIG. 1C, the electrolyte is formed from acomposite of domains of a polymer/lithium salt formulation 22 anddomains of a lithium ion conducting ceramic 28. In some cases, thelithium ion conducting material can be a garnet material such as a cubicgarnet phase Li_(6.5)La₃Zr_(1.5)Ta_(0.5)O₁₂(LLZTO), sulfides such asLi₁₀SnP₂S₁₂ (LSPS) and P₂S₅—Li₂S glass, lithium ion conducting glassceramics (LIC-GC) such as Li_(1+x+y)Al_(x)Ti_(2-x)Si_(y)P_(3-y)O₁₂,phosphates such as Li_(1.3)Ti_(1.7)Al_(0.3)(PO₄)₃ (LTAP) or Li₂PO₂N(LiPON), or combinations thereof.

A general formula for garnet materials, which can be abbreviated as(LLMO), is:

Li_(3+x)La_(3-y)A_(y)M₂O₁₂  (1)

where M can be a variety of different elements, including but notlimited to, titanium (Ti), zirconium (Zr), niobium (Nb), tantalum (Ta),antimony (Sb), bismuth (Bi) and combinations thereof, and A can also bea variety of different elements, including but not limited to, barium(Ba). Generally, x<=4 and y<=1. It is intended that the garnet materialsuseful for embodiments disclosed herein include those presently known tobe useful and those contemplated in future uses to be useful in lithiumion batteries.

As with the other solid electrolyte formulations disclosed herein, thepolymer/lithium salt formulation can reduce interfacial impedance insystems like those schematically depicted in FIG. 1C.

The formulations disclosed above have been tested in variousconfigurations. The lithium salt/polymer combinations are useful ascomponents of cathode materials and solid-state electrolyte materials.As will be apparent from the example below, PEO/PEG/LiBOB andPEO/PEG/LiTFSI perform well in both the cathode and the solidelectrolyte in enabling high cell capacity. Of course, otherformulations can enable improvements in battery performance as comparedto unloaded polymeric materials.

The following examples describe specific aspects of some embodiments ofthe invention to illustrate and provide a description for those ofordinary skill in the art. The examples should not be construed aslimiting the invention, as the examples merely provide specificmethodology useful in understanding and practicing some embodiments ofthe invention.

Examples

Preparation of Solid Electrolyte Films.

A solution of PEO, PEG, and the desired lithium salt or salts isprepared by weighing the desired ratios of solids, followed by additionof a solvent (such as acetonitrile). The solution is stirredaggressively overnight in an argon filled glove box (M-Braun, O₂ andhumidity content <0.1 ppm). A film is cast from the slurry using adoctor blade onto a Teflon substrate, and is then air-dried. The film isannealed at 100 degrees C. under vacuum for 12 hours, and then cooled. Afreestanding film can then be peeled from the substrate, and cut orpunched to the appropriate size and shape. The punched films are driedat 60 degrees C. under vacuum for about an hour.

Preparation of Cathode Films.

A stock solution containing PEO (molecular weight can be chosen based onthe desired properties of the finished structure), conductive carbonblack, and an additive lithium salt (such as LiBOB) in desired ratios(such as those identified herein) is prepared in a solvent (such asbenzonitrile) by stirring overnight. The PEO and LiBOB dissolve, whilethe carbon is suspended in the polymer/salt solution. The stock solutionis then added to an Ag₂V₄O₁₁ (“SVO”) cathode powder in the desiredamount, and the resulting suspension is stirred overnight. The resultingslurry is then coated onto a current collector, and then dried at 60degrees C. until substantially all of the solvent is evaporated. Filmsare then pressed to a desired density. The pressed cathode films aredried at 60 degrees C. under vacuum overnight prior to cell assembly.

Battery Cell Assembly.

Battery cells were formed in a high purity argon filled glove box(M-Braun, O₂ and humidity content <0.1 ppm). The silver-vanadium oxide(“SVO”) cathode film described previously and a lithium metal anodeelectrode were used. The SVO//Li pairing is typical of a primary batterychemistry. Each battery cell includes the composite cathode filmprepared as described above, a solid polymer electrolyte prepared asdescribed above, and a lithium metal anode film. No liquid electrolytecomponents were added to the battery cell. Annealing of the stack ofcathode/electrolyte films was done at 110 degrees C. on a hot plate for1 hour prior to putting in the cell with lithium and crimping the celltogether. All assembly was done under argon.

Example 1

After cell assembly, the cells were held at open current voltage for 12hours at 37 degrees C. The cells were then held at 37 degrees C. anddischarged at the desired C-rate to determine the capacity. FIG. 2 showsa comparison at C/100 for various salts formulated into the cathodeslurry and FIG. 3 shows a comparison at C/1000. The bands in each ofFIGS. 2 and 3 represent the standard deviation of the replicates of thecontrol. All solid electrolytes in the cells contained lithium triflate.Thus, FIGS. 2 and 3 compare the presence of a given lithium salt/polymerformulation in the cathode material, with a single lithium salt/polymerformulation as the electrolyte. The cathodes in FIGS. 2 and 3 wereunpressed, which is relevant because pressing cathodes prior to use willimprove the eventual performance of the battery. The additive amountsare expressed as a percentage of the amount loaded into the polymericmaterial.

FIG. 2 demonstrates that at a discharge rate of C/100, LiBOB performsbetter than the other lithium salts and better than cathodes with nolithium salt. FIG. 2 shows results from cathodes containing LiBOB thatyielded approximately 40-80 mAh/g (as compared to the theoreticalcapacity of 270 mAh/g). In combination, FIGS. 2 and 3 demonstrate thatthe capacity observed when LiBOB is incorporated into the cathode isdependent upon the discharge rate. FIG. 3 demonstrates that at a slowerrate, C/1000, formulations containing no salt can yield about 30 mAh/gof capacity. FIG. 3 shows results from cathodes containing LiBOB thatreach approximately 100 mAh/g.

Example 2

After pressing the films at greater than 1 ton/cm², the C/100 capacityreaches 220 mAh/g, which is 81% of theoretical capacity, for compositecathodes that contain LiBOB, as depicted in FIG. 4. That is, in FIG. 4,the cathode is formed with LiBOB/PEO domains as described in thesynthetic methods section above. The solid electrolyte is formed toinclude PEO/lithium triflate. The anode is based on lithium metal. AtC/1000, 88% of the theoretical capacity of this electrochemical cellarrangement is demonstrated in testing. Similar results can be achievedwhen LiTFSI is used in the composite cathode.

Example 3

Electrochemical impedance spectroscopy is used to determine the ionicconductivity of PEO/lithium salt films. A film with known thickness andarea is placed between two polished stainless steel (“SS”) disks, and anAC voltage (10 mV) is applied at varying frequencies. The resultingamplitude change and phase shift in the response is used to calculateionic conductivity of the film. FIG. 5 shows the measured ionicconductivity of PEO/lithium salt films. The concentration of the LiBOBis different by half than that of the lithium triflate (10% by weightfor LiBOB and 20% by weight for lithium triflate), but both films aresimilar in ionic conductivity. The incorporation of LiBOB or lithiumtriflate into the PEO does not result in significant changes in ionicconductivity of the film as measured in this test and depicted in FIG.5.

Example 4

Electrochemical impedance spectroscopy is used to determine the ionicconductivity of PEO/lithium salt films placed between lithium substratesinstead of the stainless steel disks of Example 3. The impedance isdetermined by where the data cross the x-axis. The impedance of filmscontaining the lithium triflate is an order of magnitude higher thanthose containing LiBOB, as depicted in FIGS. 6A and 6B (where 6B is amagnified view of the data near the origin of the plot depicted in FIG.6A). This data demonstrates that the interfacial impedance on lithiumsubstrates is reduced for PEO containing LiBOB. Thus, while FIG. 5confirmed that there was not a significant change in ionic conductivitywhen comparing LiBOB and lithium triflate, FIG. 6 shows thatpolymer/LiBOB formulations can improve the impedance performance of acathode as compared to polymer/lithium triflate formulations.

Example 5

Electrochemical impedance spectroscopy is used to determine thetime-dependence of the ionic conductivity of PEO/lithium salt filmsplaced between lithium substrates. FIGS. 7A and 7B demonstrate that theinterfacial impedance does not increase with time, indicating that apassivation film does not build up on the lithium metal due to reactionof the LiBOB with the lithium metal anode. Rather, the interfacialimpedance decreases with time when LiBOB is used, in contrast to thelithium triflate control. Electrolyte formulations containing LiBOB arestable on the reductive lithium metal surface as measured by monitoringthe impedance.

Example 6

Electrochemical impedance spectroscopy is used to determine the ionicconductivity of LLZTO/PEO/lithium salt films placed between stainlesssteel disks. In composites with PEO, LLZTO, and lithium salts,incorporation of LiBOB or LiTFSI result in a surprising increase inionic conductivity as shown in FIG. 8. LLZTO is a ceramic inclusion thatacts as an intercalation compound and facilitates ionic conductivity.However, without the lithium salt additives in the film, the LLZTO isonly somewhat effective. Surprisingly, the LiBOB and LiTFSI increasedthe effectiveness of the ceramic inclusion.

Without being bound to any particular hypothesis or mechanism of action,the addition of lithium salts (and LiBOB or LiTFSI in particular) mayincrease the presence of amorphous domains in the polymer. It ishypothesized that the softer amorphous domains (as compared to theharder crystalline domains) enable better lithium transport and alsoform better interfaces than the original (and less amorphous) polymermaterial. These better interfaces can be particularly effective in thepresence of ceramic inclusions that are added to facilitate ionicconductions, such as garnet-type ceramic inclusions.

Certain embodiments disclosed herein demonstrate improved powerperformance as compared to control and the ability to achieve nearlytheoretical capacity out of the cathode.

Certain embodiments disclosed herein demonstrate significantly lowerimpedance at the solid electrolyte/lithium metal anode interface andimproved conductivity.

Certain embodiments disclosed herein facilitate lithium salt migrationfrom a comparatively thick cathode and into a thin electrolyte, therebyincreasing the lithium salt content in the electrolyte from an initialamount of as low as 0% in the solid electrolyte.

Certain embodiments disclosed herein demonstrate that the combination ofusing LiBOB and/or LiTFSI as an additive in both the cathode andelectrolyte formulations enables high discharge capacities in an allsolid-state battery.

Various embodiments of solid electrolyte formulations disclosed hereinbenefit from the discovery of the reduction of interfacial impedancebetween a conducting polymer (such as PEO) and alithium-ion-intercalating ceramic inclusion (such as LLZTO). As comparedto prior art formulations, the present formulations use ceramicinclusions that can transport and/or intercalate lithium rather than asnon-conductive filler materials.

Notably, the formulations disclosed herein can be used in cathodeformulations. Thus, the ceramic materials that intercalate lithium andthe lithium salts that reduce interfacial impedance can be used withconducting polymers that act as binders when formulating cathodematerials.

While the invention has been described with reference to the specificembodiments thereof, it should be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the true spirit and scope of the invention asdefined by the appended claims. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,method, or process to the objective, spirit and scope of the invention.All such modifications are intended to be within the scope of the claimsappended hereto. In particular, while the methods disclosed herein havebeen described with reference to particular operations performed in aparticular order, it will be understood that these operations may becombined, sub-divided, or re-ordered to form an equivalent methodwithout departing from the teachings of the invention. Accordingly,unless specifically indicated herein, the order and grouping of theoperations are not limitations of the invention.

We claim:
 1. A lithium ion battery, comprising: an anode; a cathodecomprising an electrode active material, a first lithium salt, and anion conducting polymer material; and a solid electrolyte comprising asecond lithium salt.
 2. The battery of claim 1, wherein the firstlithium salt and the polymer material are arranged together in domainswithin the cathode, the electrode active material is arranged in domainswithin the cathode, interfaces are found where the domains of the firstlithium salt and the ion conducting polymer material and the domains ofthe electrode active material meet, and the first lithium salt is foundpreferentially at the interfaces.
 3. The battery of claim 1, wherein theion conducting polymer material comprises poly(ethylene oxide).
 4. Thebattery of claim 1, wherein the ion conducting polymer materialcomprises poly(ethylene glycol).
 5. The battery of claim 1, wherein thefirst lithium salt is selected from the group consisting of lithiumtriflate (LiCF₃SO₃), lithium tetrafluoroborate (LiBF₄), lithiumhexafluorophosphate (LiPF₆), lithium hexafluoroarsenate (LiAsF₆),lithium bromide (LiBr), lithium chlorate (LiClO₃), lithium nitrate(LiNO₃), lithium bis(oxalato)borate (LiB(C₂O₄)₂), lithiumdifluoro(oxalato)borate (LiC₂O₄BF₂), lithium metaborate (Li₂B₄O₇),lithium bis(trifluoromethanesulfonyl)imide (CF₃SO₂NLiSO₂CF₃), andcombinations thereof.
 6. The battery of claim 1, wherein the firstlithium salt comprises lithium bis(oxalato)borate (LiB(C₂O₄)₂) orlithium bis(trifluoromethanesulfonyl)imide (CF₃SO₂NLiSO₂CF₃).
 7. Thebattery of claim 1, wherein the second lithium salt is selected from thegroup consisting of lithium triflate (LiCF₃SO₃), lithiumtetrafluoroborate (LiBF₄), lithium hexafluorophosphate (LiPF₆), lithiumhexafluoroarsenate (LiAsF₆), lithium bromide (LiBr), lithium chlorate(LiClO₃), lithium nitrate (LiNO₃), lithium bis(oxalato)borate(LiB(C₂O₄)₂), lithium difluoro(oxalato)borate (LiC₂O₄BF₂), lithiummetaborate (Li₂B₄O₇), lithium bis(trifluoromethanesulfonyl)imide(CF₃SO₂NLiSO₂CF₃), and combinations thereof.
 8. The battery of claim 6,wherein the second lithium salt comprises lithium triflate (LiCF₃SO₃).9. The battery of claim 1, wherein the first lithium salt migrates intothe solid electrolyte.
 10. A lithium ion battery, comprising: an anode;a solid electrolyte comprising an ion conducting ceramic material, afirst lithium salt, and an ion conducting polymer material; and acathode.
 11. The battery of claim 10, wherein the cathode comprises asecond lithium salt.
 12. The battery of claim 10, wherein the firstlithium salt and the ion conducting polymer material are arrangedtogether in domains within the solid electrolyte, the ion conductingceramic material is arranged in domains within the solid electrolyte,interfaces are found where the domains of the first lithium salt and theion conducting polymer material and the domains of the ion conductingceramic material meet, and the first lithium salt is foundpreferentially at the interfaces.
 13. The battery of claim 10, whereinthe ion conducting polymer material comprises poly(ethylene oxide). 14.The battery of claim 10, wherein the ion conducting polymer materialcomprises poly(ethylene glycol).
 15. The material of claim 10, whereinthe ion conducting ceramic material comprises a garnet material.
 16. Thematerial of claim 10, wherein the ion conducting ceramic materialcomprises a cubic garnet phase, a sulfide glass, a lithium ionconducting glass ceramic, or a phosphate ceramic material.
 17. Thebattery of claim 10, wherein the first lithium salt is selected from thegroup consisting of lithium triflate (LiCF₃SO₃), lithiumtetrafluoroborate (LiBF₄), lithium hexafluorophosphate (LiPF₆), lithiumhexafluoroarsenate (LiAsF₆), lithium bromide (LiBr), lithium chlorate(LiClO₃), lithium nitrate (LiNO₃), lithium bis(oxalato)borate(LiB(C₂O₄)₂), lithium difluoro(oxalato)borate (LiC₂O₄BF₂), lithiummetaborate (Li₂B₄O₇), lithium bis(trifluoromethanesulfonyl)imide(CF₃SO₂NLiSO₂CF₃), and combinations thereof.
 18. The battery of claim10, wherein the first lithium salt comprises lithium bis(oxalato)borate(LiB(C₂O₄)₂) or lithium bis(trifluoromethanesulfonyl)imide(CF₃SO₂NLiSO₂CF₃).
 19. The battery of claim 11, wherein the secondlithium salt is selected from the group consisting of lithium triflate(LiCF₃SO₃), lithium tetrafluoroborate (LiBF₄), lithiumhexafluorophosphate (LiPF₆), lithium hexafluoroarsenate (LiAsF₆),lithium bromide (LiBr), lithium chlorate (LiClO₃), lithium nitrate(LiNO₃), lithium bis(oxalato)borate (LiB(C₂O₄)₂), lithiumdifluoro(oxalato)borate (LiC₂O₄BF₂), lithium metaborate (Li₂B₄O₇),lithium bis(trifluoromethanesulfonyl)imide (CF₃SO₂NLiSO₂CF₃), andcombinations thereof.
 20. The battery of claim 18, wherein the secondlithium salt comprises lithium triflate (LiCF₃SO₃).